Recovery of quadriceps muscle force following post-surgical knee immobilization is a significant therapeutic aim which is associated with quality of gait and the ability to perform activities of daily living. Several studies from various research groups have shown that neuromuscular electrical stimulation (NMES), used in conjunction with a comprehensive post-surgical rehabilitation program, is a safe and highly effective method for achieving quadriceps strengthening. The most profound results have been demonstrated with use of high intensity NMES technique in which a few very strong isometric contractions of the quadriceps muscle were performed several times per week during a physical therapy session in which the patient was seated on a biomechanical dynamometer. Efficacy of this technique has been demonstrated for individuals undergoing rehabilitation following surgical reconstruction of the anterior cruciate ligament (ACLR);however, widespread clinical acceptance of the technique has been limited. We assert that this high intensity electrical stimulation technique would be more widely practiced: 1) if a low cost, practical, cohesive system were available to replace costly and loosely connected research-based apparatus, and 2) if the system involved an NMES unit that controlled stimulation automatically using an outcome-based paradigm that did not require incessant involvement of the therapist. We propose a novel rehabilitation system indicated for quadriceps strengthening during post-surgical knee immobilization in which the knee joint will be stabilized using an instrumented post-surgical knee brace and stimulation is delivered by a high output, portable NMES unit with autonomous, adaptive stimulation control capabilities. The target markets for this device would be clinics who serve patients undergoing rehabilitation following ACLR or total knee arthroplasty (TKA). The target price for the system will be $4000. The goals of this FastTrack SBIR project are therefore to demonstrate feasibility of the adaptive stimulation control approach in Phase I using laboratory-based apparatus. We will interface our adaptive stimulator to the KinCom dynamometer and show that the stimulator can elicit a contraction of sufficient strength that function outcomes could be expected, and demonstrate that the adaptive controller can develop appropriate stimulation patterns for use in this low-cycle count application. The Phase II goals will be: 1) to develop an instrumented knee brace capable of stabilizing the knee during near maximal isometric contractions and obtaining measurements of the resulting torque;2) to implement a rapid training version of our adaptive stimulation controller that is suited for use in this low cycle count application;3) to implement an alternate fundamental stimulation waveform that may be more comfortable to some users;and 4) to demonstrate efficacy of the proposed system for quadriceps strengthening following ACLR or TKA. / Relevance The proposed work may benefit public health through development of an electrical stimulation exercise device indicated for quadriceps strengthening during post-surgical immobilization following surgical repair of the anterior cruciate ligament (ACLR) or total knee arthroplasty (TKA). Quadriceps strengthening has been shown to improve gait and improve performance of activities of daily living (ADLs). There are approximately 100,000 ACLR and 400,000 TKA surgeries per year in the United States.